1. Field of the Invention
This invention relates to a vehicle steering control system.
2. Description of the Related Art
Prior art references proposed by the assignee, including those made public by Japanese Laid-Open Patent Application Nos. Hei 5(1993)-197423 and Hei 9(1997)-221054, teach vehicle steering control system technologies that provide steering angle assistance for keeping the vehicle on a desired course of travel along a lane of a road.
By providing fine steering assistance while preventing vehicle lane wandering, these technologies greatly reduce the burden on the vehicle driver, which tends to increase particularly during long, high-speed driving on an expressway or the like.
In view of the interference or interaction between this type of steering assistance control and vehicle driver steering, the control should preferably be effected to provide assistance through torque (steering force) rather than steering angle.
However, when a lane-keeping-steering torque assist control of such type is conducted using an actuator such as an electric motor of a conventional power-steering torque assist control system such that both the lane-keeping-steering torque assist control and the power-steering torque assist control are conducted using the same actuator, there may be a case when the two kinds of control interfere with each other, thereby affecting the vehicle driver's perception of vehicle steering response.